Re: 4HDD Raid5 - 2 Disk fails

[Adam Goryachev <mailinglists@websitemanagers.com.au>]

On 04/10/12 19:33, Dominique wrote:
> Hi,
>
> I am writing here out of desperation, and lost hope. I have a NAS with
> a 4 HDD Raid 5 setup. A week ago, we suffered a power outage that
> seemed to have fried 2 of the 4 disks at the same time. I say seemed,
> since I have some contradictory information: 3 of the 4 power leds are
> still active, the web interface shows only 2 of 4 disks, and cli
> information shows that disk sda is partially answering, sbd and sdc
> are ok, sdd seems to be totally dead.
>
> Don't ask about the backup.
>
> Is there anything I can do to get sda back to some life to save what
> can be saved ?
My limited suggestions:
1) Since this is the state of the drive after a power cycle, probably
another power cycle won't be any worse...
Remove the drive, and connect to a standard linux machine, also connect
a brand new identical (size) drive
Use dd_rescue to attempt to copy as much as possible from the dead drive
to the new drive
Add the new drive back to the NAS, and use some CLI magic to re-create
the raid array pretending that it is all clean
Do a backup

You should try the dd_rescue ASAP, this could easily take a few days
depending on the amount of damage, and the size of the drive. If this
fails, then forget about the rest of the steps.... and start looking for
backups, or perhaps attempt a professional data recovery agency (very
expensive).

For how to do the dd_rescue, ask google, there are very good information
on this already, just ensure to use the gnu dd_rescue.

Regards,
Adam

-- 
Adam Goryachev
Website Managers
www.websitemanagers.com.au